Field of the Invention
The present invention relates to a control apparatus for an internal combustion engine. In particular, the invention relates to the control apparatus for the internal combustion engine that can use alcohol fuel.
Description of the Related Art
Known internal combustion engines for vehicles or automobiles include a bifuel-type internal combustion engine that can use alcohol fuel as substitute fuel. A vehicle including such an internal combustion engine is called an FFV (Flexible Fuel Vehicle). In the internal combustion engine as described above, alcohol fuel such as methanol or ethanol as well as hydrocarbon fuel such as gasoline can be used individually or can be mixed together.
Japanese Patent Laid-Open No. 2009-47071 discloses a hybrid vehicle including a bifuel-type internal combustion engine in which the stoppage of an internal combustion engine is followed by the cranking of an internal combustion engine by a motor/generator to remove the residual moisture in an exhaust pipe by scavenging. The purpose of this is to exclude the adverse effect by the residual moisture due to the fact that the residual moisture causes a deteriorated catalyst warming performance during the restart of the internal combustion engine after the stoppage.
Japanese Patent Laid-Open No. 2002-256919 discloses a hybrid vehicle including a general internal combustion engine that is not the bifuel-type one. In this hybrid vehicle, during the fuel cutting in deceleration, a motor and a power generator are used to drive an engine to remove the residual exhaust gas in a range from the intake pipe to the catalyst by scavenging.
By the way, when the low-temperature start of the internal combustion engine is followed by the running for a relatively-short time (i.e. short trip), this generally causes, after the stoppage of the running, the condensation of water in the exhaust, thereby causing a large amount of aqueous droplets attached to the inner wall of an exhaust passage. When the internal combustion engine is the bifuel-type one in particular, the above tendency is remarkable because the combustion of alcohol fuel causes a higher amount of water when compared with the case of hydrocarbon fuel such as gasoline.
In such a case, the aqueous droplets attached to the inner wall of the exhaust passage may flow down and may be collected and frozen in a relatively-small space between an exhaust valve and a valve sheet. The ice due to this freezing is disadvantageous in that this ice is continuously attached to at least one of the exhaust valve and the valve sheet even after the subsequent restart of the internal combustion engine, thereby resulting in a defective opening of the exhaust valve.
According to one solution to this problem as disclosed in Japanese Patent Laid-Open No. 2009-47071, the stoppage of the internal combustion engine is followed by the cranking (or motoring) of the internal combustion engine by another motor to remove aqueous droplets attached to the inner wall of the exhaust passage by scavenging.
However, on the other hand, the motoring requires power consumption, thus requiring the motoring time of the motoring to be optimally set to the minimum required time.
With regard to this, Japanese Patent Laid-Open No. 2009-47071 discloses, from the viewpoint that an increase of the fuel alcohol concentration causes an increase of the residual moisture in the exhaust pipe is, to set a longer cranking period in accordance with the increase of the fuel alcohol concentration.
However, the technique disclosed in Japanese Patent Laid-Open No. 2009-47071 does not intend to solve the problem specific to the invention of this application as described above (i.e., the freezing due to the running for a relatively-shot time after the low-temperature start of the internal combustion engine and thus the defective opening of the exhaust valve after the restart due to this). Thus, even the application of the technique disclosed in Japanese Patent Laid-Open No. 2009-47071 cannot provide an optimal setting of the motoring time after the stoppage of the internal combustion engine.
The present invention has been made in view of the above situation. It is an objective of the invention to provide a control apparatus for an internal combustion engine that can optimally set the motoring time after the stoppage thereof in an internal combustion engine in which alcohol fuel can be used.